GASES (Part 3)

Gas Laws A Quick Review Of What We’ve Learned

Boyle’s Law P α 1/V This means Pressure and Volume are INVERSELY PROPORTIONAL if moles and temperature are constant. For example, P goes up as V goes down. P 1 V 1 = P 2 V 2. Robert Boyle ( ). Son of Earl of Cork, Ireland. Nice lipstick, dude!

Charles’s Law If n and P are constant, then V α T V and T are directly proportional. V 1 V 2 = T 1 T 2 If one temperature goes up, the volume goes up! If one temperature goes up, the volume goes up! Jacques Charles ( ). Isolated boron and studied gases. Balloonist. Somebody’s got a case of the Mondays

Gay-Lussac’s Law If n and V are constant, then P α T P and T are directly proportional. P 1 P 2 = T 1 T 2 If one temperature goes up, the pressure goes up! Joseph Louis Gay- Lussac ( ) Balloons make me Happy!

Combined Gas Law If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law! Boyle’s Law Charles’ Law Gay-Lussac’s Law = P1P1 V1V1 T1T1 P2P2 V2V2 T2T2

IDEAL GAS LAW Brings together gas properties. BE SURE YOU KNOW THIS EQUATION! P V = n R T

Gases in the Air The % of gases in air Partial pressure (STP) 78.08% N mm Hg 20.95% O mm Hg 0.94% Ar 7.1 mm Hg 0.03% CO mm Hg P AIR = P N + P O + P Ar + P CO = 760 mm Hg Total Pressure760 mm Hg

Dalton’s Law of Partial Pressures What is the total pressure in the flask? P total in gas mixture = P A + P B +... Therefore, P total = P H 2 O + P O 2 = 0.48 atm Dalton’s Law: total P is sum of PARTIAL pressures. 2 H 2 O 2 (l) ---> 2 H 2 O (g) + O 2 (g) 0.32 atm 0.16 atm 0.32 atm 0.16 atm

Dalton’s Law John Dalton

Gases and Stoichiometry 2 H 2 O 2 (l) ---> 2 H 2 O (g) + O 2 (g) Decompose 1.1 g of H 2 O 2 in a flask with a volume of 2.50 L. What is the volume of O 2 at STP? Solve a gas law stoichiometry problem just like any other stoichiometry problem…the unit you want to go to goes on top…the unit you want to get rid of goes on bottom.

Gases and Stoichiometry 2 H 2 O 2 (l) ---> 2 H 2 O (g) + O 2 (g) Decompose 1.1 g of H 2 O 2 in a flask with a volume of 2.50 L. What is the volume of O 2 at STP? Solution 1.1 g H 2 O 2 1 mol H 2 O 2 1 mol O L O 2 34 g H 2 O 2 2 mol H 2 O 2 1 mol O 2 34 g H 2 O 2 2 mol H 2 O 2 1 mol O 2 = 0.36 L O 2 at STP

Gas Stoichiometry: Practice! A. What is the volume at STP of 4.00 g of CH 4 ? 4.00 g CH 4 x 1 mole CH4 x 22.4 L = 5.58 L 16.05g CH4 1 mole B. How many grams of He are present in 8.0 L of gas at STP? 8.0 L He x 1 mole x 4.00g He = 1.4 g He 22.4 L 1 mole He

Gases and Stoichiometry (cont.) IS NOT STP If the problem IS NOT at STP… 1.Do an A to B stoichiometry problem solving for moles of the “B” compound 2.Use PV = nRT to solve for the variable